The present invention relates to a pumping arrangement in general, and more particularly to an arrangement for pumping fluids which is equipped with a control arrangement which is so constructed as to prevent overloading of the drive of the pumping arrangement.
There are already known various pumping arrangements of the type here under consideration, and usually such arrangements include one or more pumps which is or are driven by a drive, such as an internal combustion engine. It is also known, in such pumping arrangements, to provide an auxiliary pump which discharges control fluid at a rate corresponding to the speed of the drive, a throttle or flow restrictor being provided in the discharge conduit of the auxiliary pump. It is known from these arrangements that, when the throttle or flow restrictor is of a fixed flow-through cross-sectional area, the pressure in the discharge conduit upstream of the throttle will vary proportionately to the square of the speed of rotation of the auxiliary pump which, in turn, is at a fixed ratio to the speed of rotation of the drive. Thus, the pressure in the discharge conduit upsteam of the throttle will give an indication of the speed of rotation of the drive. It is already known from the prior art to utilize the pressurized fluid in the discharge conduit of the auxiliary pump for displacing a control slide or a similar valve between two positions of the same, the control slide being interposed into the control circuit of the respective pump so as to control flow of fluid therethrough in such a manner that, when the pressure in the discharge conduit of the auxiliary pump exceeds a predetermined level, the variable-output pump is adjusted toward higher output, and conversely when the pressure in the discharge conduit drops below a predetermined value.
In such conventional control arrangements for controlling the output of a variable-output pump, the flow-through cross-sectional area of the throttle, which determines the pressure with which the control fluid in the discharge conduit of the auxiliary pump acts on the control slide, and a force exerted on the control slide by a spring which urges the control slide against the action of the pressurized fluid, are so selected relative to one another that, when the speed of rotation of the drive decreases by a certain amount with respect to a predetermined operating value, the force of the spring overcomes the force exerted by the pressurized fluid in the discharge conduit, and the control slide is displaced into a position in which the output of the variable-output pump is decreased. One of the main disadvantages of these prior-art constructions is that the control arrangement is only responsive to the speed of rotation of the drive, and does not depend at all on other operating conditions thereof, such as the power input to the drive, which may result in a situation where the drive may be overloaded during some phases of operation of the pumping arrangement, while it may operate under less than optimum utilization conditions during other phases of operation of the pumping arrangement.